High-density recording on multiple tracks of a magnetic tape is known. In certain arrangements, parallel tracks extend along a longitudinal direction of the magnetic tape. Magnetic tape is moved transversely across a magnetic head so that a read and/or write gap of the magnetic head is moved in proximity to the desired track. During a recording or playback, the head needs to stay in position as the tape moves in a longitudinal direction across the read/write cap. To increase storage capacities to meet increased demands, track density, which is the number of tracks per distance (e.g., inches), has been increased. As this track density increases, the track pitch and width decrease. For proper read/write operation, the magnetic head must stay at, or very near, the center line of the track. Due to this reduced track pitch, improvements to the head positioner are needed to minimize the offset between the head and the center line of the track. One important feature of such a position is that it allows the drive to monitor the head-to-track relationship. If the drive determines that the head and track are offset, then the head positioner corrects the relative position to maintain the relationship between the head and the center line of the track.
Closed loop positioners are often used in tape systems having higher track densities. In high-density tape systems, the tape may wander in the lateral direction as it moves in the longitudinal direction, which results in an offset between the magnetic head and the track center line. To avoid these types of problems, tape cartridges for high-density tape drives are preformatted with information often called servo information, which is used to maintain the correct lateral position of the tape with respect to the magnetic head. Servo information provides the system with feedback to communicate to the system the continuous position of the tape. Servo information can alert the system about the occurrence of an offset. Based on the information that an offset has occurred, the head is moved by a positioner to the center line of the track so that write/read operations can occur properly.
Closed loop positioners use “fine positioners” to move the head during a write/read operation. These fine positioners are used to maintain the position of the head at the center line of the track under a closed loop servo control using the preformatted servo information on the tape. Fine positioners generally include a head-carriage assembly, which comprises a magnetic head, a top head carriage, a voice coil motor, and a bottom head carriage.
The tracking servo system employed by linear tape drives, such as the LTO (Linear Tape Open) family, for example, increases the track density. Track density is one of the parameters, besides bit density, that allows storage capacity to increase. The tracking servo system requires feedback to indicate the relative position of the tape and the recording head elements. One of the methods employed in linear tape drives using such feedback signals is to pre-record a series of magnetic stripes that contain position feedback information, which is a timing based signal. When the stripes are recorded with predetermined azimuth angles, the signals from the head can be processed to decode the lateral position information regarding the relative position of the head and the tape.
The decoding of the lateral position information is based on timing of the detected pulses. As the magnetic head moves up and down relative to the tape, the timing of the pulses changes indicating the position feedback signal. This decoding process relies on the precise pre-recording of the servo stripe pulses without any written-in tape speed fluctuations. Such fluctuations can result in position errors, which would cause the tracking servo system to erroneously react to the fluctuations. For example, if the speed of the tape fluctuates while writing servo stripes, the timing based signal used in the position feedback information will be incorrect when the tracking servo system reads the pre-recorded servo stripes. Based on this erroneous information, the tracking servo system will erroneously react and mis-position the magnetic head with respect to the tape.